Wind Shear over Forested Areas

d = displacement distance h = tree height U = wind speed Uref = wind speed at reference measurement height z = measurement height above ground zref = reference measurement height z0 = surface roughness HE installation of wind turbines within forested areas presents many problems. These include correctly characterizing the hub height wind resource and wind shear, determining the energy production from a wind turbine and estimating the level of turbulence and associated loads. This paper adds to the knowledge-base regarding wind shear in forested areas as it affects resource assessment. SODAR data from a forested island offshore of Maine are used to estimate mean shear characteristics and wind turbine power production and to evaluate shear models over forested areas. The mean shear and power production estimates show that shear at this site is much different than might be expected and that it has a significant effect on power production estimates. The best-fit parameters for three models are used to determine if and when they might be generally applicable to forest canopy shear flows. The result show that all of the models can be used to characterize 10-minute averaged wind shear at this site, but that none of the three models result in a consistent set of parameters that could be used to predict wind shear if the appropriate parameters for the site are unknown. Further investigation shows that the model parameters at this site are a function of time of day, wind speed and wind direction.